Constructing built-in electric fields in bimetallic selenide heterojunctions to bidirectional catalyze polysulfide conversion for flexible lithium-sulfur batteries

Parasitic shuttle effects and sluggish kinetics severely limit the practical applications of lithium-sulfur (Li–S) batteries. Developing conducting catalysts with high catalytic activity is effective strategy to address such issues. Electronic engineering as tuning strategy can optimize the electronic structure and enhance the redox reaction kinetics. Herein, NiSe₂-CoSe₂ hollow microspheres with abundant heterogeneous interfaces were synthesized as sulfur cathode catalysts. DFT calculations show that heterostructure can promote electron redistribution and form built-in electric field (BIEF), which causes the directional transfer of electrons. Additionally, NiSe₂-CoSe₂ has optimized adsorption energy, which can effectively suppress shuttle effect. Meanwhile, electrochemical tests further confirmed bidirectional catalytic ability. Benefiting the merits, S/NiSe₂-CoSe₂-GO-CNF (S/NiCo-GN) achieved an initial discharge specific capacity of 1353.35 mAh g⁻¹ at 0.2C and stable 1000 cycles at 1C with a capacity decay rate of only 0.044 % per cycle. Moreover, S/NiCo-GN also achieved high areal capacity of 1.688 mAh cm⁻² at 0.5C under high loading (∼2.5 mg cm⁻²) and lean electrolyte (∼10 μL mg⁻¹) conditions. The flexible pouch cell further demonstrated its high safety, good thermal stability, and robust mechanical stability. This work provides guiding methods for the design of efficient catalysts, which can contribute to the realisation of high-performance Li–S batteries.